We have been using
RV Headsets for the past three years and love them. Yes, hand signals, cell phones, walkie-talkies, etc. will all do the job and we have used them all but find the RV Headsets to be the easiest to use and most useful. They are not without drawbacks (local radio playing through then for one) but we have found them so much better than the other options. You can talk in a normal voice, hands-free, and have the ability to talk and hear at the same time. They are expensive but we feel well worth it.